NEW YORK – Obese patients without diabetes who underwent gastric bypass showed a surprisingly high prevalence of hyperinsulinemic hypoglycemia starting about a year following bariatric surgery, based on anecdotal experience at one U.S. center.
"We have no data on the prevalence, but it is turning out to be a very prevalent side effect of gastric bypass. All of a sudden at the University of Minnesota these patients are queued up to get into our clinic," Dr. John P. Bantle said at the annual ADA Advanced Postgraduate Course.
Dr. John P. Bantle
"I know of about 25 or 30 cases reported in the literature, but I’ve seen more than that many cases myself. They’re taking over my clinic," said Dr. Bantle, an endocrinologist and professor of medicine at the University of Minnesota in Minneapolis.
"The only thing that protects against patients developing this is preexisting diabetes. Patients who had diabetes [before undergoing gastric bypass surgery] don’t get this because there needs to be a strong insulin response" to ingestion of carbohydrates, something that patients with a history of inadequate insulin production don’t mount. "It happens in people who have healthy insulin-producing beta cells and can make a robust response to postprandial hyperglycemia," he said.
The likely cause is the rapid transit of food between the stomach and small intestine that gastric bypass creates. "Carbohydrates are absorbed much more quickly than nature intended," producing an acute hyperglycemic episode that provokes a strong hyperinsulinemia. That, in turn, brings on a sharp hypoglycemia that can cause the patient to pass out. It is a form of dumping syndrome that does not appear as quickly following bariatric surgery as other manifestations of dumping syndrome, he said.
An alternative explanation, which Dr. Bantle calls much less likely, is that gastric bypass changes the blood level of glucagonlike peptide–1, leading to beta-cell hyperplasia and hyperinsulinemia.
This type of hypoglycemia does not occur in patients who have their pylorus intact following bariatric surgery, such as those who undergo gastric banding or receive a gastric sleeve, he said.
In addition to a delay of more than a year following surgery before it appears, other features that characterize this postprandial hypoglycemia include normal fasting glucose and serum insulin levels, and a carbohydrate-triggered plasma glucose level of less than 50 mg/dL accompanied by a serum insulin level that exceeds 50 microU/mL.
The best treatment is carbohydrate avoidance or restriction, Dr. Bantle said. If that proves impossible, patients can try taking acarbose with a meal that contains carbohydrates. They can also have one or two glucose pills ready to take at the first sign of hypoglycemic symptoms, he said.
Dr. Bantle said that he is a consultant to Unilever, and serves as a speaker for Eli Lilly, Merck, and Novo Nordisk.